Due to the nature of diesel engines, they require some extra help when first starting up at a cold temperature. The glow plug is a heating element that is activated during startup when the temperature of the engine is too low. It raises the temperature inside the cylinders to facilitate in pressurizing and detonating the diesel fuel. The system typically makes the driver wait around 10 seconds while the plugs warm up the engine. Once the correct temperature has been achieved, the computer will then let the driver start the engine.
What the diesel engine pre-glow light means
Normally, the glow plug indicator light will come on only when the engine is cold. Typically, this light flashes only when an issue has been detected.
The most common reason to replace glow plugs is age. Over time, after repeated warm up cycles, the glow plugs age and are not able to produce any heat. Replacing any malfunctioning glow plugs should get rid of any issues you are having. If a new glow plug doesn’t remedy the problem, take a look at other parts of the circuit, mainly the timer. The timer’s job is to turn the plugs off once the correct temperature has been reached. A faulty timer may keep the plugs on for too long, wearing them out, or even not turn the plugs on at all.
If a fault has been detected, the computer will save a code in its memory to help diagnose the issue. Have a certified technician hook up a scan tool to your car to read this code.
Is it safe to drive with the diesel engine pre-glow light on?
Some vehicle engines cannot even be started until the glowplug light has turned off, therefore preventing the drivers from starting the engine too soon. You should always wait for the light to shut off before attempting to start the engine. Being a little patient will help keep your engine going strong in the long run.
Our certified technicians are always available if you ever require assistance identifying glow plug issues.
This article originally appeared on YourMechanic.com as What Does the Diesel Engine Pre-Glow Warning Light Mean? and was authored by Spencer Cates.